MWM-Array and MR-MWM-Array Eddy Current Testing for Piping and Vessels
Conference: Publication Date: 1 April 2019Testing Method:
The MWM®-Array and MR-MWM-Array are eddy current sensor arrays with single or dual rectangle drive
configurations and linear arrays of inductive or magnetoresistive sensing elements. This presentation describes a
range of applications for these sensors including stress/strain imaging/monitoring, corrosion imaging (internal and
external) with and without coatings, insulation or fireproofing for piping, vessels and structures, and crack detection
and depth measurement for fatigue and stress corrosion cracking. These solutions use multivariate inverse methods
with precomputed databases called HyperLattices that enable estimation of multiple unknown properties of interest
such as magnetic permeability, lift-off, pipe wall thickness, insulation thickness and weather jacket properties. The
unique approach improves robustness to variations in field conditions (e.g. insulation sagging that causes substantial
variation in insulation thickness around a pipe, or temperature variations that make inspection during operation
challenging, or surface conditions that make crack or pit depth measurement more difficult). Handheld and larger
portable instruments are also described that are uniquely capable of providing reliable imaging of multiple unknown
properties (as required for reliable corrosion imaging through coatings or difficult surface conditions). These
instruments provide simultaneous measurement of all channels in the arrays (no multiplexing) to enable improved
image reliability and even rescaling of crack responses for cracks falling between channels. Furthermore, impedance
values at up to three frequencies are recorded simultaneously at every sensing element. This is essential for reliable
correction for uncontrolled variations, such as changes in lift-off (sensor proximity to the surface) and/or magnetic
permeability, to provide accurate pipe wall thickness measurement for example. Basic methods are described along
with practical application results.
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